Braun tube



E. RUSKA BRAUN TUBE Aug. 3o, 1938,

Filed Aug. 5, 1936 Patented Aug. 30, 1938 UNITED STATES Arr orties BRAUN TUBE Application August 5,

In Germany 6 Claims.

In order to attain ample energy for the deflected ray and for example an attendant great luminosity on the luminous screen in electron ray tubes of the type wherein the ray is cross deiiected, e. g. as in oscillograph tubes, picture transmitting tubes and receiving tubes, accompanied at the same time by small expenditure for the magnetic. or electrical cross-control fiel-ds, the proposal has been made to supply energy by means of a so-called retarded accelerating eld ("Nachbeschleunigungsfeld) to the already low velocity controlled ray and to effect said object without deleteriously affecting the degree of its existing deection.

In the embodiments of such arrangements hitherto used, it has however appeared that the retarded acceleration was always associated with a decrease in the deflectional angle and hence in the deflection on the luminous screen. In order to attain the original degree of deflection the ray therefore had to be deflected in the crosscontrol eld to a greater angular degree. This, in addition to the occasional very appreciable expenditure involved in the stronger cross-control fields required, also had the very inconven- .ient drawback that the distortions in the rayy cross-section (image element on the luminous screen) which rapidly increase as the deflectional field increases, occur o-ven in portions of the screen which are relatively near to the center.

It is the object of the present invention more or less appreciably to obviate this decrease in sensitivity hitherto associated with retarded acceleration and even to attain an increase in sensitivity by means of the retarded accelerating iield.

The known types of retarded accelerated fields which have been fundamentally tested as to serviceability and which have an approximately plane extent of level surface are produced, for example, by a current-traversed resistance layer disposed on the inner Wall of the tubes and which extends either vin the form of a conical convolution along the bulb or else is formed as a homogeneous layer. 'I'he retarded accelerating elds may also be produced by a number of annular electrodes separated from each other and which are gradually brought to increasingly higher potentials the nearer the individual rings approach the screen.

The lines of force of the retarded accelerating l `iields should extend as much as possible towards the ray-.deflecting pivot point in the entire field domain. The fulfillment of this condition is 4difficult however in the neighborhood `of the de- 1936, Serial No. 94,433 August 7, 1935 (Cl. Z50-27.5)

liecting system. At that point a eld is always formed which subsequently tends to decrease the angular deflection of the ray already produced by the cross-control system;v The result is a sagging of the accelerated level surface from the luminous screen, that is, in a direction convexly towards the cathode, and exactly ,the reverse of what is required for satisfactory retarded acy celeration. Although the voltage within the thus deviated level surface and traversed by the electrons is relatively small comp-aredwith the total voltage of the retarded accelerating eld, nevertheless the corresponding decrease in` original ray deection becomes quite noticeable` on the screen since, rst, the electron ray hasa relatively low velocity in the critical domain and suliers a relativelyvpowerful angular deflection and, because, secondly, the leverage with respect to the screen is greatest at this point and makes itself noticeable through a definiteangular de,- crease `and hence in a great reduction in the spot deflection on the screen.

In order to obviate these drawbacks the invention, when applied to magnetically cross-deflected and magnetically or electrically concentrated electron ray bundles, proposes' to permit the electron ray to pass through a tube having the same or nearly the same potential as the negative end of the retarded accelerating iield and extending into said field and thus to place the end of the anode tube facing the luminous screen at a lower potential difference relative to the screen than is the beginning of the accelerating field, that is, to place the end of the anode tube somewhat in the interior of the accelerating field.

A plane passing through the end of the anode tube and perpendicular to the tube axis will therefore strike the periphery of the tube at level surfaces which are already more or less positive with respect to the potential of the anode tube. These potentials should therefore under no conditions lie in the vicinity of the positive end of the retarded accelerating field since otherwise the rays within the cross-control field will attain appreciably -diierent speed depending on the degree of cross-deflection involved and thus produce a deection which is insensitive asr a whole and of non-linear extent.

In order to give the level surfaces of the retarded acceleration system (which are at anode potential), a` slightly convex shape facing the screen the anode tube is provided at one end with a capof approximately hemispherical shape which is provide-d with a diaphragm opening for permitting passage and also limitation of the ray.

Two embodiments of the invention subject matter are illustrated in the drawing.

Fig. 1 showsr a longitudinal section of a Braun tube.

Fig. 2 is a section through the deflecting chamber of the tube.

The tube, at the end of the tube neck I, is provided with a. ray producing system 2 to which the anode tube 3 is attached. The anode tube is provided with a cap 4 at its front end, said cap hav,k ing a ray limiting opening 5.

The interior wall of the tube neck is provided with a conducting coating 6 or an annular electrode which is at anode potential or, if desired, even at a more negative potential than` can be assigned to the anode potential. The edge of the short circuiting ring 6 (annular electrode) which faces the luminous screen and which isat anode potential and which cuts off the retarded accelerating eld lies further removed from screen 'I than the end of anode tube 3 having the ray limiting diaphragm 5. A free annular space between anode tube 3 and the tube wall draws the level surfaces into itself, these lying against the anode tube andv being indicated by dash lines, and thereby improves the spread of the level surfaces in the `space in front of the anode tube. The term level surfaces, is used to denote isopotential eld strength planes.

The magnetic cross-control which must obviously lie behind the ray limiting diaphragm 5 occurs, when the accelerating eld is designed in accordance with the invention, in a space occupied by the accelerating field, nevertheless the average electron velocity in the cross-control field is only inappreciably increased compared to the inlet velocity. Since the dis-tributed shape of the eld is favorable for cross-control purposes, the advantages incident to retarded acceleration may be utilized without the therewith associated drawback of loss of sensitivity. Inasmuch as a slight increase in deflectional field strength .is frequently accompanied by a no longer industrially permissible expense, the introductionofthe.retarded accelerating field according to the invention means that rst the degree of retarded acceleration (retarded acceleration voltage/preliminary or anode voltage) can be chosen so high that the great advantages inherent in the use of retarded accelerati-on can be especially well utilized.

Concentration of the ray in systems according to the invention may be effected electrically or magnetically. A magnet coil 8 may, according to Fig. 1, be forced either outwardly over the tube neck I or else wound in the inside of the tube around'the end of the anode tube 3 as shown'in the dotted lines, two disks 9, I being first fastened to this tube by spot welding at distances corresponding to the desired length of coil. Electrical concentration of the ray is effected according to Fig. 2 preferably by means of -an annular electrode II negatively charged with respect to the tube and located shortly in front of the opening 5 of the anode tube 3 and within the interior thereof, the field of said electrode facing the cathode being screened by means of a perforated disk I2 which is at anode potential. The potential increases between the negative annular electrode I I and the apertured diaphragm 5 in the anode tube, and likewise also after the ray has passed the apertured diaphragm. The shape of all positive level surfaces,- considering their potential values with respect tothe anode, is convex towards the screen and hence favorable to cross deflection. In this arrangement in contrast to the system using magnetic ray concentration there occurs no undesired deformation of the accelerated potential surfaces since all of these are curved convexly towards the screen. In the case of magnetic ray concentration some few level surfaces are located directly adjacent the anode potential which are drawn into the opening of the anode tube diaphragm. These however exert a slight ray concentrating refracting power which therefore is insufficient to focus the ray. This function is rather assumed by the magnet coil,

The anode tube 3 of the invention is preferably adapted to be positively centered, together with the accelerating system, on a cross yoke I3 which is fastened as by spot welding to the center of a Spread ring band I 4. The spread ring permits the entire system to be anchored rigidly in the tube neck I without requiring any special arrangement. In constructing .the anode system of Fig. 2 the anode tubeV 3 is centered with respect to a hole in the cross yoke by means of about three bent-overlugs through which an anode cap I5 provided with external threads and collar is inserted from the screen side. An internally threaded insulating screw ring I8 locks both the anode cap andanode tube together with the cross yoke which is fastened to the-spread ring. The control electrode fastened to the press foot and the cathodeare screwed intothe insu` lating screw mount I8 and thereby centered with respect to the anode system whereupon the press foot is fused together with the tube neck. 'I'he inside thread of the insulating ring I8 is recessed in the center so as to obtain as high a strike-over voltage of the accelerating system as possible.; The tube according to the invention may therefore as a whole (inclusive of anode voltage andacceleration voltage) beV operated at very high operating voltages (2O kv. and greater) without excessively increasing the ampere turns necessary for magnetic cross control.

The resistance `layer I6 used for producing the homogeneous acceleration eld extends from the short circuiting ring I'I near screen l over the conical or bowed bulb'to far within the bulb neck I `at the point on which subsequently the spread ring I4 acts as lead-in electrode for conveying the anode voltage.- Obviously this point of the neck i may also be preliminarily metallized in order to insure positive contact with the high ohmic layer -IE on the one hand and the spread ring It (ancde system) on the other hand.

The short circuiting ring II near the screen is preferably made broad in order to impart a good convex shape to the level surfaces near and facing the screen.

I claim:

1 .A Braun tube having therein an electron gun comprising a cathode, a control electrode, and an anode, said control electrode having an exteriorly threaded portion directed toward said anode, said anode having an exteriorly threaded portion directed toward said control electrode, an insulating ring having an interiorly threaded portion adapted to engage said controlv electrode and a second interiorly threaded portion adapted to engage said anode, said insulating ring having its inner surfacebetween said interiorly threaded portions recessed to a diameter substantially greater than said threaded portions.

l 2. In combination with a cathode ray tube having a tubular neck portion enclosing electron gun elements substantially as described in claim 1, an annular conducting shield positioned within said neck, a cylindrical metal element, having one closed end, positioned within said shield and having a central aperture disposed through said closed end adapted to it around said threaded anode portion and be held thereby betweensaid anode and said insulating ring.

3. In combination with a cathode ray tube having a tubular neck portion surrounding electron gun elements substantially as described in claim 1, a cylindrical metallic shield disposed within said neck portion, an annular supporting diaphragm disposed in Contact with said shield centrally arranged to `lit around said threaded anode portion, and a cylindrical anode tube having one end terminated by an apertured diaphragm portion similarly arranged to t over said threaded anode portion, whereby said insulating ring, said supporting diaphragm, said anode tube, and said anode may be held together by the threadable cooperation of said anode and said insulating ring.

4. In combination with a cathode ray tube havingfa tubular neck portion surrounding electron gun elements substantially as described in claim 1, a cylindrical metallic shield disposed within said neck portion, an annular supporting diaphragm disposed in contact with said shield centrally arranged to fit around said threaded anode portion, and a cylindrical anode tube having one end terminated by an apertured diaphragm portion similarly arrangedv to t over said threaded anode portion, whereby said insulating ring, said supporting diaphragm, said anode tube, and said anode may be held together by the threadable cooperation of said anode and said insulating ring, the other end of said cylindrical anode tube having a centrally apertured diaphragm and a centrally apertured hemispherical cap.

5. In combination with a cathode ray tube having a tubular neck portion surrounding eleotIOn gun elements substantially as described in claim 1, a cylindrical metallicA shield disposed within said neck portion, an annular supporting diaphragm disposed in contact with said shield centrally arranged to lit around said threaded anode portion, and a cylindrical anode tube having one end terminated by an apertured diaphragm portion similarly arranged to t over said threaded anode portion, whereby said insulating ring, said supporting diaphragm, said anode tube, and said anode may be held together by the threadable cooperation of said anode and said insulating ring, the other end of said cylindrical anode tube having a centrally apertured diaphragm and a centrally apertured hemispherical cap, and an annular electrode disposed in axial alinement with said anode tube within said hemispherical cap.

6. In combination with a Braun tube having an envelope enclosing an electron gun, having a cathode, an anode, and a control electrode, positioned at one end thereof and an oppositely disposed fluorescent screen, a cylindrical shield disposed Within said tube knear said gun, a supporting diaphragm connecting said shield and said anode, a cylindrical anode tube, xedly associated with said anode, having at the end opposite thereto an apertured diaphragm, a centrally apertured hemispherical cap, and an annular electrode disposed Concentrically within said cap; a high resistance layer fixed upon the inner surface of said envelope connected to said cylindrical shield and extended therefrom toward said fluorescent screen, and an annular unipotential electrode disposed in contact with said high resistance layer near but not in contact with said fluorescent screen.

' ERNST RUSKA. 

